The Chronicles of Narnia books and movies have so many beautiful images (or descriptions of images) that it's not surprising people would be inspired to theme their wedding around the franchise. In addition, given the snowy atmosphere often presented in the books, it's a great wedding idea for winter weddings.
Some brides seem to go with more traditional dresses for a Narnia wedding, and others go for old-fashioned looking, or otherworldly dresses. Since this is a more common theme for winter weddings, some brides choose warmer dresses.
For a Narnia themed wedding, wintery and moody decor, especially that inspired by winter trees, is ideal: